Complex systems, such as large communications systems and the like are inevitably subject to failure. At the same time customer satisfaction and simple economics dictate that these systems be available all or nearly all of the time. Network operators and network equipment suppliers often refer to this as high availability systems or service meaning that a significant percentage of customers that utilize these systems will ordinarily find that the services are available.
Manufacturers or equipment suppliers often resort to redundant equipment or redundant subsystems to insure that the systems are available. Generally there are two types of redundancy that are employed. One referred to as 2n or more generally xn redundancy means that for every system or subsystem that is operational or in use often referred to as a primary system or subsystem there is at least one system or subsystem or more generally x−1 redundant or standby systems or subsystems. The second may be referred to as n+1 or more generally n+m redundancy meaning that for every n systems or subsystems that are operational or primary there is one additional standby system or subsystem or more generally m additional standby systems or subsystems. Of course you can utilize a combination such as 2n+1 redundancy where every primary system has one redundant system plus there is one additional redundant system.
The problem that all of these redundancy schemes suffer from is that in the event of a failure of one of the units, either a primary or a standby unit or system the level of redundancy suffers until the failed unit or system is again available. One unattractive solution is simply to increase the level of redundancy to the point that some number of failures can be experienced and still maintain sufficient redundancy to handle any problems or further failures that may occur during resolution of the initial faults or failures. Unfortunately these additional units or systems or subsystems can be an economic burden due of course to there direct cost but also overhead costs such as power supply and physical space plus periodic maintenance or in sum life cycle costs.
Clearly a need exists for methods and apparatus that is suitable for supporting and maintaining redundant equipment requirements by dynamically reallocating available resources for redundant functionality.